by Jayne O'Donnell and Oliver St. John, USA TODAY

by Jayne O'Donnell and Oliver St. John, USA TODAY

Sales made in the post-Christmas rush to redeem retail gift cards or make returns could help an otherwise lackluster shopping season meet rosy estimates for holiday sales.

The International Council of Shopping Centers said Wednesday that retail sales for the week ended Dec. 22 were up just 0.7%, but the group says it's sticking to its forecast for a 3% increase in sales for the whole holiday season.

The ICSC estimate is in contrast to the 0.7% sales increase MasterCard Advisors research chief Michael McNamara said it saw in the two months leading up to Christmas. MasterCard's estimate is for sales using cash, checks and all credit cards in key holiday categories, including luxury goods, clothing, electronics and furnishings, as well as online sales. Still, McNamara says, it represents just 30% to 35% of the U.S. retail sales except for cars, groceries and restaurants.

Last year, MasterCard's estimate for the same period was up 2%. The official National Retail Federation tally of 2011's sales, however, showed they were up 5.6%.

McNamara did note that sales the week after Christmas account for about 15% of holiday sales, so that could brighten the picture. And the NRF is sticking to its estimate that holiday sales will be up 4.1%.

"One of the biggest weeks of the holiday season is just beginning, and we are looking to Washington to come together in these crucial moments to avert going over the fiscal cliff," NRF CEO Matt Shay said. "Consumers' mixed confidence so far this holiday season has been evident, but we still believe we are on pace for decent growth overall."

Marion Posen, 53, shopped at the Lansdale, Pa., Kohl's store on Wednesday, where she hoped to find items on sale that she'd seen on Saturday. Despite a spate of inclement weather keeping checkout lanes wide open, she says the store had sold out of the items she hoped to buy.

"Their stock had been depleted, definitely. But I found other things," said Posen, who left with two shirts and two sweaters.

When shoppers show up to redeem gift cards and return or exchange gifts, they often spend far more than the value of the gifts or cards. Gift cards are the most popular last-minute gifts, according to a Consumer Reports poll. And their sales aren't counted until they are redeemed.

Cashing in gift cards and returning wrong sizes the day after Christmas has been a tradition for Kelsey Heinze, 25, and her sister Sarah, 23, since they were old enough to drive. On Wednesday, the crowds at the King of Prussia Mall, one of the largest malls in the country, located outside Philadelphia, were "very pleasant until the hour of noon, and after that complete chaos," said Kelsey. Her favorite buy: an emerald pencil skirt from J. Crew, an exchange for the same item in the wrong size.

Shoppers got off to a slow start in December, following a busy - and long - Black Friday shopping period. But they got their second wind and stepped up their shopping the week ended Dec. 15, ICSC chief economist Michael Niemira said.

He wasn't sure the momentum would carry through the few days leading up to Christmas, however. Wintry weather in much of the country may have kept some shoppers home.

McNamara agrees the big winter storm that hit northern areas of the country may well have kept people home but could have helped online sales.

According to Chase's Holiday Pulse survey, online sales from Oct. 29 to Christmas were up 15.2% over last year. Sales volume for transactions settled on Dec. 23 was up 124% over last year.

"You're seeing merchants enabling last-minute shopping, and that's driving a lot of traffic from consumers who want to purchase late in the game," says Shaun Abraham, strategic initiatives director for Chase Paymentech.

Online sales Christmas Day were up 22.4% over Christmas 2011, according to the IBM Digital Analytics Benchmark, out Wednesday. All those new iPads may have paid off for other retailers. The iPad drove more retail shopping than any other mobile device - with 12.5% of online sales.

Niemira said the weekly sales were being compared with a week last year that included Christmas Eve, so he expects the current week's sales will be boosted even more by the calendar shift. His group is holding to its prediction of a 4% to 4.5% increase in December retail sales and a 3% increase overall for the holiday season.